1. Field of the Invention
The present invention relates to a novel squarylium compound, a method for producing the same and an infrared absorbent.
2. Description of the Related Art
Near-infrared absorbents are utilized in a variety of applications including optical films such as infrared ray cut films or heat ray shielding films for plasma display panels or charge coupled devices (CCDs), photothermal conversion materials for recordable optical discs or flash welding development materials, information display materials for security inks or invisible bar code inks. As for required performance characteristics, these infrared absorbents should exhibit high absorbability to infrared light or an infrared region, while exhibiting as low an absorbability to a visible region as possible (invisibility). In addition, robustness is required.
At present, cyanine methine pigments are provided as infrared absorbing pigments with superior invisibility. However, long methine conjugated chains readily react with heat, oxygen, nucleophiles and the like and are decomposed, and are generally considered to exhibit low robustness. Meanwhile, vanadylphthalocyanine pigments are provided as pigments with high robustness. However, the vanadylphthalocyanine pigments have insufficient invisibility. Accordingly, infrared absorbents exhibiting both invisibility and robustness have been required for a long period of time.
Recently, a squarylium compound has been provided as a material satisfying these requirements (Japanese Patent Application Laid-Open (JP-A) Nos. 2000-159776 and 10-36695). This squarylium compound exhibits excellent infrared absorbability, invisibility and robustness.
Meanwhile, when a compound having a higher wavelength range of absorption region (infrared region) is provided, a receiver can widely select an absorption wavelength range of infrared absorbing materials suitable for applications or products.